As navigation using mobile devices, such as global positioning system (GPS) devices and smartphones equipped with GPS capability, becomes increasingly ubiquitous, the demand for extending this functionality indoors is on the rise. GPS, however, does not work well indoors as the satellite signals tend to be too weak indoors. Presently there exist a number of approaches to provide the indoor navigation functionality.
One approach is to utilize information provided by inertial navigation system (INS) that use low-cost inertial sensors and magnetometers, which are typically embedded in many mobile phones nowadays. Nevertheless, using these sensors to provide an indoor navigation solution tends to be problematic. For example, low-cost microelectromechanical system (MEMS) sensors tend to drift and diverge in a few seconds, resulting in inaccuracy. This alone may be enough reason to explain why such approach is not widely used today.
Another approach is to constrain the navigation results by mounting the sensors on the foot of a user and imposing zero velocity updates to the inertial calculation. However, mounting the sensor on the foot is not practical in many cases, for example when using a handheld device.
Another approach is to use a pedometer, which is an algorithm that count steps and estimate the trajectory according to the step length and the device attitude. However, there are several problems associated with this approach. Firstly, this approach depends very much on the way the user holds the mobile device. There is typically an assumption that the mobile device's attitude relative to the user's body is constant. This assumption renders this approach very limiting and not robust. Secondly, this approach depends on the length of the step of the user, which is unknown. Thirdly, this approach tends not to use most of the accelerometer information.
The Detailed Description references the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference like features and components.